package com.hmdp.utils;

import cn.hutool.core.util.BooleanUtil;
import cn.hutool.core.util.StrUtil;
import cn.hutool.json.JSONObject;
import cn.hutool.json.JSONUtil;
import lombok.extern.slf4j.Slf4j;
import org.springframework.data.redis.core.StringRedisTemplate;
import org.springframework.stereotype.Component;

import java.time.LocalDateTime;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;
import java.util.function.Function;

import static com.hmdp.utils.RedisConstants.*;

@Component
@Slf4j
public class CacheClient {
    private final StringRedisTemplate stringRedisTemplate;

    private static final ExecutorService CACHE_REBUILD_EXECUTOR = Executors.newFixedThreadPool(10);

    public CacheClient(StringRedisTemplate stringRedisTemplate) {
        this.stringRedisTemplate = stringRedisTemplate;
    }

    public void set(String key, Object value, Long time, TimeUnit unit) {
        stringRedisTemplate.opsForValue().set(key, JSONUtil.toJsonStr(value), time, unit);
    }

    public void setWithLogicExpire(String key, Object value, Long time, TimeUnit unit) {
        RedisData redisData = new RedisData();
        redisData.setData(value);
        redisData.setExpireTime(LocalDateTime.now().plusSeconds(unit.toSeconds(time)));
        stringRedisTemplate.opsForValue().set(key, JSONUtil.toJsonStr(redisData));
    }

    /**
     * 缓存空对象解决缓存穿透
     *
     * @param keyPrefix  前缀
     * @param id
     * @param type       返回值类型
     * @param dbFallback 回调函数，即查询数据库的方法
     * @param time       时间单位
     * @param unit
     * @param <R>
     * @param <ID>
     * @return
     */
    public <R, ID> R queryWithPassThrough(String keyPrefix, ID id,
                                          Class<R> type,
                                          Function<ID, R> dbFallback,
                                          Long time, TimeUnit unit) {
        //1 从redis中查询缓存
        String key = keyPrefix + id;
        String json = stringRedisTemplate.opsForValue().get(key);
        //2 判断是否存在
        if (StrUtil.isNotBlank(json)) {
            //3 存在，直接返回
            return JSONUtil.toBean(json, type);
        }
        //判断命中的是否是空值
        if (json != null) {
            return null;
        }
        //4 不存在，根据id查询数据库
        R r = dbFallback.apply(id);
        //5 若数据不存在
        if (r == null) {
            //将空值写入redis,解决缓存穿透问题
            stringRedisTemplate.opsForValue().set(key, "", CACHE_NULL_TTL, TimeUnit.MINUTES);
            //返回null
            return null;
        }
        //6 存在，先将数据写入redis,加入过期时间
        this.set(key, r, time, unit);
        //7 返回
        return r;
    }

    /**
     * 逻辑过期解决缓存击穿
     * 需要提前将热点数据加载进redis缓存
     */
    public <R, ID> R queryWithLogicExpire(String keyPrefix, ID id,
                                          Class<R> type,
                                          Function<ID, R> dbFallback,
                                          Long time, TimeUnit unit) {
        //1 从redis中查询缓存
        String key = keyPrefix + id;
        String json = stringRedisTemplate.opsForValue().get(key);
        //2 判断是否存在
        if (StrUtil.isBlank(json)) {
            //3 不存在，直接返回
            return null;
        }
        //4 存在，需要先把json反序列化为对象
        RedisData redisData = JSONUtil.toBean(json, RedisData.class);
        R r = JSONUtil.toBean((JSONObject) redisData.getData(), type);
        LocalDateTime expireTime = redisData.getExpireTime();
        //5 判断是否过期
        if (expireTime.isAfter(LocalDateTime.now())) {
            //5.1 未过期，直接返回店铺数据
            return r;
        }
        //5.2 已过期，需要重建缓存
        //6 缓存重建
        //6.1 获取互斥锁
        String lockKey = LOCK_SHOP_KEY + id;
        boolean isLock = tryLock(lockKey);
        //6.2 判断是否获取锁成功
        if (isLock) {
            //开启独立线程，实现缓存重建
            CACHE_REBUILD_EXECUTOR.submit(() -> {
                try {
                    //查询数据库
                    R r1 = dbFallback.apply(id);
                    //写入redis
                    this.setWithLogicExpire(key, r1, time, unit);
                } catch (Exception e) {
                    throw new RuntimeException(e);
                } finally {
                    unlock(lockKey);
                }
            });
        }
        //6.4 当前线程直接返回过期商铺信息
        return r;
    }

    private boolean tryLock(String key) {
        Boolean flag = stringRedisTemplate.opsForValue().setIfAbsent(key, "1", 10, TimeUnit.SECONDS);
        return BooleanUtil.isTrue(flag);
    }

    private void unlock(String key) {
        stringRedisTemplate.delete(key);
    }

}
